Apparatus for injection molding a ceramic greenware composite without knit lines

ABSTRACT

A method and apparatus for injection molding of ceramic suspensions is disclosed wherein an elastomeric bladder is disposed within a mold cavity of a mold. The elastomeric bladder, in a relaxed state, can be tubular or can be formed by bonding together sheets of material. A ceramic suspension is injected into the elastomeric bladder, whereby the elastomeric bladder is distended. Distention of the elastomeric bladder applies a significant force to the ceramic suspension for preventing jetting and formation of knit lines within the ceramic suspension. The ceramic suspension distends the elastomeric bladder until the mold cavity is filled. The ceramic suspension is then exposed to conditions sufficient to cause the injected ceramic suspension to form a molded ceramic greenware composite. The molded ceramic greenware composite can then be removed from the mold for drying and for debindering and densification to form a finished ceramic part.

CROSS-REFERENCE TO RELATED APPLICATION

This is a divisional of application Ser. No., 07/534,821 filed Jun. 7,1990 is now U.S. Pat. No. 5,098,620.

RELATED PATENT

This is a divisional of U.S. Pat. No. 5,098,620, filed Jun. 7, 1990.

BACKGROUND OF THE INVENTION

Ceramic parts are commonly produced by injection of a ceramic suspensioninto a mold and then treated to form a molded ceramic greenwarecomposite. The molded ceramic greenware composite is subsequentlyremoved from the mold for further processing to form the finishedceramic part. Injection molding typically requires that the ceramicsuspension be injected into a mold cavity having a cross-section whichis larger than a conduit through which the ceramic suspension isdelivered. The ceramic suspension is typically cohesive enough to form astream during mold-filling which will break apart, or jet, and fold uponitself to form knit lines as it fills the mold cavity. The ceramicsuspension often does not recombine intimately at these knit lines,which can thereby form structural flaws that limit the performance ofthe finished ceramic part.

A molded ceramic greenware composite that has been formed by injectionmolding is removed from the mold cavity for further processing toproduce the finished ceramic part. When using certain binder systems,such as aqueous methylcellulose formulations, stresses caused byhandling a rubbery gelled ceramic greenware composite can causeirregularities in the molded ceramic greenware composite after gellatinof the methylcellulose. In addition, molded ceramic greenware compositesprepared using these aqueous-based binder systems must be dried at acontrolled rate to prevent formation of drying cracks before the moldedceramic greenware composite is further processed and densified. Moldsalso often cause seams to form in molded ceramic greenware compositeswhich must be removed during finishing steps. Further, the mold cavityoften must have a surface which is highly polished in order to produce aceramic part having an acceptable finish. The ceramic suspension canalso deleteriously affect the mold, such as by abrasive wear of a moldcavity wall, thereby limiting the usable life of the mold.

Thus, a need exists for an improved ceramic injection molding method andapparatus for forming molded ceramic greenware composites which overcomeor minimize the aforementioned problems.

SUMMARY OF THE INVENTION

The present invention relates to a method and apparatus for injectionmolding a ceramic suspension to form a molded ceramic greenwarecomposite.

A method for injection molding a ceramic suspension to form a moldedceramic greenware composite includes injecting the ceramic suspensioninto an elastomeric bladder disposed within a mold cavity defined by amold, whereby the elastomeric bladder is distended by the ceramicsuspension. The distention of the elastomeric bladder thereby causes theelastomeric bladder to apply a significant force to the ceramicsuspension to prevent jetting of the ceramic suspension and formation ofknit lines within the ceramic suspension. The injected ceramicsuspension is exposed to conditions sufficient to form the moldedceramic greenware composite.

Apparatus for injection molding a ceramic suspension to form a moldedceramic greenware composite includes a mold defining a mold cavity andan elastomeric bladder disposed within the mold cavity for receiving theceramic suspension. Means for injecting the ceramic suspension into theelastomeric bladder inject the ceramic suspension into the elastomericbladder, whereby the elastomeric bladder is distended. Distention of theelastomeric bladder causes the elastomeric bladder to apply significantforce to the ceramic suspension for preventing jetting of the ceramicsuspension and formation of knit lines within the ceramic suspension.Means for exposing the injected ceramic suspension to conditionssufficient to form the molded ceramic greenware composite expose theinjected ceramic suspension to conditions sufficient to form the moldedceramic greenware composite.

Molded ceramic greenware composites can thereby be formed from a ceramicsuspension without jetting or formation of knit lines within the ceramicsuspension. Finished molded ceramic parts are thus formed havingsubstantially reduced numbers of structural flaws. Further, the moldedceramic greenware composites formed can be removed from the mold withoutadhesion of the molded ceramic greenware composite to the mold. Inaddition, the bladder adds stiffness to the molded ceramic greenwarecomposite, thereby reducing distortion of the molded ceramic greenwarecomposite. Also, because the finish of the molded ceramic greenwarecomposite is not determined by the mold, a polish between the mold andmolded ceramic greenware composite is not required. Elimination ofcontact between the molded ceramic greenware composite and the mold canalso prolong the useful life of the mold.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 is a section view of one embodiment of the invention wherein anelastomeric bladder is disposed in a relaxed state within a mold cavitydefined by a mold.

FIG. 2 is a section view of the embodiment of FIG. 1 wherein theelastomeric bladder has been evacuated.

FIG. 3 is a section view of the embodiment of FIGS. 1 and 2 duringinjection of a ceramic suspension into the evacuated elastomeric bladderfrom a ceramic suspension source.

FIG. 4 is a section view of the embodiment of FIGS. 1-3 wherein theinjected ceramic suspension has filled the mold cavity.

FIG. 5 is a side view of the elastomeric bladder of FIGS. 1-4 containinga molded ceramic greenware composite formed from the injected ceramicsuspension. The elastomeric bladder is sealed at an inlet end and at anoutlet end for drying of the molded ceramic greenware composite.

FIG. 6 is a section view of a second embodiment of the present inventionwherein the elastomeric bladder is formed of two sheets of materialdisposed within a mold cavity defined by a mold and wherein theelastomeric bladder is supported within the mold cavity at an inlet endand an outlet end of the elastomeric bladder.

FIG. 7 is a plan view of the embodiment of FIG. 6 illustrating aperipheral seal of the elastomeric bladder and a flange disposed aboutthe elastomeric bladder.

FIG. 8 is a section view of the embodiment of FIGS. 6 and 7 duringinjection of a ceramic suspension into the elastomeric bladder.

DETAILED DESCRIPTION OF THE INVENTION

The above features and other details of the method and apparatus of theinvention will now be more particularly described with reference to theaccompanying drawings and pointed out in the claims. The same numberpresent in different figures represents the same item. It will beunderstood that the particular embodiments of the invention are shown byway of illustration and not as limitations of the invention. Theprinciple features of this invention may be employed in variousembodiments without departing from the scope of the invention.

In one preferred embodiment of the present invention, shown in FIG. 1,an injection molding apparatus 10 includes an elastomeric bladder 12 ina relaxed state. Elastomeric bladder 12 can be tubular in the relaxedstate. Elastomeric bladder 12 has an inlet end 16 and an outlet end 18and is disposed within a mold cavity 20 of mold 22. Mold cavity 20 isdefined by mold cavity walls 24 and 26 of mold 22. Mold halves 28 and 30of mold 22 are held in an assembled position, as shown in FIG. 1, bymold clamps 32 and 34. Inlet end 16 of elastomeric bladder 12 issupported between fill tube 36 and nozzle bushing 38. Fill tube 36provides fluid communication between a nozzle 40 and elastomeric bladder12. Valve 42 at nozzle 40 provides fluid communication between a ceramicsuspension source 44 and fill tube 36, and regulates flow of a ceramicsuspension 46 from ceramic suspension source 44 through nozzle 40 toelastomeric suspension source 44 through nozzle 40 to elastomericbladder 12. Outlet end 18 of elastomeric bladder 12 is supported betweena vacuum tube 48 and a split core 50. Vacuum tube 48 provides fluidcommunication between elastomeric bladder 12 and a vacuum source 52.Vents 54 provide fluid communication between mold cavity 20 and theatmosphere. A heat transfer fluid can be conducted through channels 56in mold 22 to thereby control the temperature of ceramic suspension 46introduced to elastomeric bladder 12.

In a preferred embodiment, a method for injection molding a ceramicsuspension to form a molded ceramic greenware composite includesdisposing elastomeric bladder 12 within mold cavity 20 of mold 22, asshown in FIG. 1. Vacuum can be applied to evacuate elastomeric bladder12 through vacuum tube 48 by vacuum source 52. Elastomeric bladder 12thereby collapses, as can be seen in FIG. 2. Evacuation of elastomericbladder 12 maximizes contact between elastomeric bladder 12 and ceramicsuspension 46 and prevents development of air pockets within elastomericbladder 12 during injection of ceramic suspension 46 into elastomericbladder 12. As shown in FIG. 3, ceramic suspension 46 is injected intoelastomeric bladder 12 through nozzle 40 and fill tube 36. Elastomericbladder 12 is distended during injection of ceramic suspension 46.Distention of elastomeric bladder 12 causes elastomeric bladder 12 toapply a significant force to ceramic suspension 46 within elastomericbladder 12, thereby preventing jetting of ceramic suspension 46 andformation of knit lines within ceramic suspension 46. Injection ofceramic suspension 46 into mold cavity 20 directs elastomeric bladder 12against mold cavity walls 24 and 26. Ceramic suspension 46 is injectedinto mold cavity 20 until elastomeric bladder 12 and ceramic suspension46 conform to mold cavity 20, as shown in FIG. 4. Air or other gas isdisplaced from mold cavity 20 through vents 54 by injection of ceramicsuspension 46 into elastomeric bladder 12.

Continued injection of ceramic suspension 46 into elastomeric bladder 12through fill tube 36 after mold cavity 20 is filled, will direct ceramicsuspension 46 from elastomeric bladder 12 through vacuum tube 48. Valve42 is closed upon filling of mold cavity 20 with ceramic suspension 46.Pressure within elastomeric bladder 12 during injection of ceramicsuspension 46 is at least partially determined by the cross-sectionalarea of vacuum tube 48. For example, pressure within elastomeric bladder12, when mold cavity 20 has been filled by ceramic suspension 46, can beincreased by reducing the cross-sectional area of vacuum tube 48. Oncemold cavity 20 has been filled, vacuum through vacuum tube 48 can besecured, either before or after valve 42 is closed. Vacuum can besecured by sealing vacuum tube 48 from vacuum source 52 by a suitablemeans, such as by closing a valve, not shown, or by terminating thevacuum source. The temperature of mold 22 and ceramic suspension 46 canbe controlled by conducting a heat transfer fluid through channels 56.

Ceramic suspension 46 includes a ceramic powder and a binder system. Theceramic powder, as that term is used herein, can include, for example:ceramics, such as alumina, silicon carbide, silicon nitride, aluminumnitride, boron nitride, boron carbide and zirconia. Powders other thanceramic which can be used with the disclosed process include cermets,such as chromium-alumina; powdered metals, such as ferrous-based alloys;etc. The binder system includes a suitable binder and a suitablecarrier. The binder can comprise, for example, an organic material, suchas methylcellulose, wax, etc. The binder can also comprise athermoplastic. Suitable carriers include water and organic solvents,such as methanol, methyl ethyl ketone, etc.

Elastomeric bladder 12 can be formed of polyurethane or otherelastomeric material. Elastomeric bladder 12 can, in the alternative, beformed of an elastic material. In a preferred embodiment, elastomericbladder 12 is formed of an elastomeric material which is relativelyabrasion resistant, resilient and which exhibits high extensibility. Anexample of a suitable elastomeric material includes polyurethane, suchas aromatic polyether polyurethane. In a preferred embodiment, thethickness of elastomeric bladder 12 is in the range of between about onemil (2.54×10⁻³ cm) and about ten mils (25.4×10⁻³ cm). Elastomericbladder 12 is permeable by the selected carrier in the binder system ofthe ceramic suspension. In a particularly preferred embodiment,elastomeric bladder 12 has a thickness of about one mil (2.54×10⁻³ cm)and has a water vapor permeability of less than about one hundred andforty grams per twenty-four hours through a one hundred square inchmatrix area at a temperature of about 50° C.

Mold 22 can be formed of a thermally conductive material, such as steel,aluminum, etc. The temperature of ceramic suspension 46 can becontrolled in mold 22, for example, by conducting a suitable heattransfer fluid through channels 56 in mold 22. For a ceramic suspension46 which includes an aqueous methylcellulose polymer binder system, thetemperature of ceramic suspension 46 within elastomeric bladder 12during injection is maintained in the range of between about 1° C. andabout 25° C. Means for injection of ceramic suspension 46 from ceramicsuspension source 44 can be, for example, a reciprocating screw, notshown. Ceramic suspension 46 can be heated within mold cavity 20 to gelthe binder, whereby the binder comes out of solution to provide rigidityto ceramic suspension 46. Molded ceramic greenware composite 58, isthereby formed from ceramic suspension 46. Molded ceramic greenwarecomposite 58 is sufficiently rigid for removal from mold cavity 20without substantial distortion.

Where the binder is a thermoplastic, the temperature of ceramicsuspension 46 within mold cavity 20 during injection can be maintainedin the range of between about 30° C. and about 60° C. Means forinjecting ceramic suspension 46 can be, for example, a plunger-typemachine, not shown. Mold 22 can be cooled for cooling of ceramicsuspension 46 to a temperature in the range of, for example, betweenabout 1° C. and about 25° C. Ceramic suspension 46 thereby forms moldedceramic greenware composite 58, which is sufficiently rigid for removalfrom mold cavity 20 without substantial distortion.

In another preferred embodiment, mold 22 is formed of amicrowave-transparent material. Examples of microwave-transparentmaterials include thermoplastics, such as polyetherimine (PEI) andthermosets, such as a polyurethane tooling resin system formed of, forexample, a polymeric methylenediisocyanate solution and a polyolsolution. Gellation of binder in ceramic suspension 46 can be achievedby application of microwave energy where, for example, ceramicsuspension 46 includes an aqueous methylcellulose polymer binder system.Molded ceramic greenware composite 58 can thereby be formed from ceramicsuspension 46 by application of microwave energy to ceramic suspension46. Molded ceramic greenware composite 58 is sufficiently rigid forremoval from mold cavity 20 without substantial distortion.

Molded ceramic greenware composite 58 and elastomeric bladder 12 arethen removed from mold cavity 20 by releasing mold clamps 32 and 34 anddisassembling mold halves 28 and 30. Elastomeric bladder 12 is sealed atinlet end 16 and outlet end 18. Inlet end 16 and outlet end 18 ofelastomeric bladder 12 are sealed, as shown in FIG. 5, by heat-sealing,or by another suitable method. Heat sealing can be accomplished bysqueezing inlet end 16 and outlet end 18 between bars, not shown, whichare sufficiently hot to soften elastomeric bladder 12 and seal inlet end16 and outlet end 18.

Molded ceramic greenware composite 58 is then dried by a suitablemethod, such as by disposing molded ceramic greenware composite 58 insuitable oven, not shown. The carrier is volatilized in the oven andtransported across elastomeric bladder 12, thereby drying molded ceramicgreenware composite 58 to form a dried, molded ceramic greenwarecomposite. For example, where the binder system is an aqueousmethylcellulose polymer binder system, molded ceramic greenwarecomposite 58 within elastomeric bladder 12 elastomeric bladder 12 can bedried at a temperature of between about 30° C. and about 70° C.Elastomeric bladder 12 is then removed from the dried, molded ceramicgreenware composite 58. A finished, molded ceramic part is then formedby suitably debindering the dried, molded ceramic greenware compositeand then densifying the debindered, molded ceramic greenware compositeby a suitable method, e.g., sintering.

In another preferred embodiment of the present invention, shown in FIG.6, an injection molding apparatus 60 has an elastomeric bladder 62 whichcan be formed by sheets 64 and 66. Elastomeric bladder 62 also has aninlet end 70 and an outlet end 72. Sheets 64 and 66 are supported withinmold 74 between mold halves 76 and 78.

Elastomeric bladder 62 can be formed of a material which is permeable towater moisture vapor. In a preferred embodiment, the material has athickness of between about one mil and about ten mils. In a particularlypreferred embodiment, the material has a permeability to water vapor ofless than about one hundred and forty grams per twenty-four hoursthrough a one hundred square inch (645 cm²) surface area at atemperature of about 50° C. An example of a suitable material is apolyurethane, such as an aromatic polyether polyurethane.

Mold 74 is maintained in an assembled condition by mold clamps 80 and82. Elastomeric bladder 62 is disposed within mold cavity 84, which isdefined by respectively. Mold 74 can be formed of a thermally conductivematerial, such as steel, for example, or of a microwave-transparentmaterial. One example of a suitable microwave-transparent material ispolyetherimide. Another example is a polyurethane tooling resin, such asa polyurethane tooling resin system formed from a polymericmethylenediisocyanate solution and a polyol solution.

Inlet end 70 of elastomeric bladder 62 is supported between fill tube 90and mold halves 76 and 78. Fill tube 90 provides fluid communicationbetween a nozzle 92 and elastomeric bladder 62. Valve 94 at nozzle 92provides fluid communication between a ceramic suspension source 44 andelastomeric bladder 62, and can regulate the flow of ceramic suspension46 from ceramic suspension source 44 into elastomeric bladder 62. Outletend 72 is supported between a vacuum tube 100 and mold halves 76 and 78.Vacuum tube 100 provides fluid communication between elastomeric bladder62 and vacuum source 52. Vents 104 provide fluid communication betweenmold cavity 84 and the atmosphere. A heat transfer fluid can beconducted through channels 106 for controlling the temperatures of mold74 and of ceramic suspension 46 within elastomeric bladder 62.

Sheets 64 and 66 can be bonded together to form a peripheral seal 108,shown in FIG. 7, by heat-sealing or by some other conventional method.Flange halves 110 and 112 can be disposed about peripheral seal 108 ofelastomeric bladder 62 for preventing puckering of elastomeric bladder62 during injection from a ceramic suspension source 44 of a ceramicsuspension 46 into elastomeric bladder 62.

In a preferred embodiment, a method of injection molding a ceramicsuspension to form a molded ceramic greenware composite includes drawingvacuum within elastomeric bladder 62 through vacuum tube 100 by vacuumsource 52. Evacuation causes collapse of elastomeric bladder 62, as seenin FIG. 6, to thereby maximize contact between elastomeric bladder 62and ceramic suspension 46 during injection of ceramic suspension 46.Ceramic suspension 46 is injected from ceramic suspension source 44through nozzle 92 and fill tube 90 into elastomeric bladder 62, therebydistending elastomeric bladder 62, as shown in FIG. 8.

As elastomeric bladder 62 is distended, a significant force is appliedby elastomeric bladder 62 to ceramic suspension 46 within elastomericbladder 62, thereby preventing jetting of ceramic suspension 46 andformation of knit lines within ceramic suspension 46. Air or other gaswithin mold cavity 84 of mold 74 is displaced by elastomeric bladder 62and ceramic suspension 46 through vents 104. Continued distention ofelastomeric bladder 62 by injection of ceramic suspension 46 directselastomeric bladder 62 against mold cavity wall 86. Elastomeric bladder62 and ceramic suspension 46 within elastomeric bladder 62 therebyconform to mold cavity walls 86 and 88.

Ceramic suspension 46 is directed through vacuum tube 100 when moldcavity 84 has been filled. Pressure within elastomeric bladder 62 is atleast partially limited by the cross sectional area of vacuum tube 100.When ceramic suspension 46 has filled mold cavity 84, valve 94 is closedto secure flow of ceramic suspension 46 into elastomeric bladder 62.Once mold cavity 84 has been filled, vacuum through vacuum tube 100 canbe secured either before or after valve 94 is closed. Vacuum can besecured by sealing vacuum tube 100 from vacuum source 52 by a suitablemeans, such as by a valve, not shown, or by terminating the vacuumsource. Nozzle 92 is then disconnected from fill tube 90 and elastomericbladder 62. Vacuum tube 100 is disconnected from vacuum source 52.

Ceramic suspension 46 is then exposed to conditions sufficient to formmolded ceramic greenware composite 114, such as is described forformation of molded ceramic greenware composite 58 in the embodimentillustrated in FIG. 5. Molded ceramic greenware composite 114 can thenbe removed from mold 74. Inlet end 70 and outlet end 72 of elastomericbladder 62 can then be sealed by a suitable method, such as heatsealing. Molded ceramic greenware composite 114 within elastomericbladder 62 can then be dried by sufficiently heating molded ceramicgreenware composite 114 to cause moisture within molded ceramicgreenware composite 114 to volatilize and thereby be transported acrosselastomeric bladder 62. Flange halves 110 and 112 and elastomericbladder 62 are then removed from dried molded ceramic greenwarecomposite 114. Puckering of elastomeric bladder 62 at flange halves 110and 112 can be trimmed from dried molded ceramic greenware composite 114during removal of elastomeric bladder 62 from dried molded ceramicgreenware part 114. Dried molded ceramic greenware composite 114 canthen be debindered and densified to form a finished molded ceramic part.

EQUIVALENTS

Those skilled in the art will recognize, or be able to ascertain usingno more than routine experimentation, many equivalents to the specificembodiment of the invention described specifically herein. Suchequivalents are intended to be encompassed in the scope of the followingclaims.

We claim:
 1. An apparatus for injection molding a ceramic suspension toform a molded ceramic greenware composite, comprising:a) a mold defininga mold cavity; b) an elastomeric bladder disposed within the moldcavity, the elastomeric bladder having an inlet end for receiving theceramic suspension and an outlet end for evacuating said elastomericbladder and for limiting force applied to the ceramic suspension by saidelastomeric bladder; c) means for injecting the ceramic suspension intosaid elastomeric bladder, whereby the elastomeric bladder is distended,said distention of the elastomeric bladder causing the elastomericbladder to apply sufficient force to the ceramic suspension tosubstantially prevent jetting of the ceramic suspension and formation ofknit lines within the ceramic suspension during injection of the ceramicsuspension into the elastomeric bladder; and d) means for exposing theinjected ceramic suspension to conditions which are sufficient to formthe molded ceramic greenware composite.
 2. An apparatus of claim 1further comprising a fill tube and a nozzle at the inlet end of theelastomeric bladder, and a vacuum tube and a split core at the outletend of the elastomeric bladder for supporting the elastomeric bladderwithin the mold cavity.
 3. An apparatus of claim 2 wherein the means forinjecting the ceramic suspension into the elastomeric bladder is areciprocating screw-type injection molding machine.
 4. An apparatus ofclaim 2 wherein the means for injecting the ceramic suspension into theelastomeric bladder is a plunger-type injection molding machine/
 5. Anapparatus of claim 4 wherein the elastomeric bladder is tubular in arelaxed state.
 6. The apparatus of claim 4 wherein the elastomericbladder comprises two sheets which are bonded together to form aperipheral seal.
 7. The apparatus of claim 6 further comprising a flangedisposed about the peripheral seal for preventing puckering of theelastomeric bladder during injection of the ceramic suspension.
 8. Theapparatus of claim 7 wherein the mold defines vents for providing fluidcommunication between the mold cavity and the atmosphere, therebyallowing discharge of gas from the mold cavity during injection of theceramic suspension into the elastomeric bladder.
 9. The apparatus ofclaim 8 wherein the mold defines channels for conducting a heat transfermedium through the mold, thereby allowing control of the temperature ofthe ceramic suspension within the elastomeric bladder.
 10. The apparatusof claim 9 wherein the elastomeric bladder is permeable to water vaporand has a water vapor permeability of less than about one hundred andforty grams per twenty-four hours through a one hundred square inchmatrix area at a temperature of about 50° C. when the elastomericbladder has a thickness of about one mil.
 11. The apparatus of claim 10wherein the elastomeric bladder comprises polyurethane.
 12. Theapparatus of claim 11 wherein the polyurethane comprises an aromaticpolyether polyurethane.
 13. The apparatus of claim 12 wherein the moldcomprises steel.
 14. The apparatus of claim 12 wherein the mold istransparent to microwaves.
 15. The apparatus of claim 14 wherein themold comprises a thermoplastic.
 16. The apparatus of claim 15 whereinthe thermoplastic comprises polyetherimine.
 17. The apparatus of claim14 wherein the mold comprises a thermoset.
 18. The apparatus of claim 17wherein the thermoset comprises a polyurethane tooling resin system. 19.The apparatus of claim 18 wherein the polyurethane tooling systemcomprises a polymeric methylenediisocyanate solution and a polyolsolution.
 20. In an injection molding apparatus for receiving a ceramicsuspension and for molding the ceramic suspension to form a moldedceramic greenware composite:the improvement comprising an elastomericbladder disposed within a mold cavity of a mold for receiving a ceramicsuspension injected into the mold cavity of the mold, the elastomericbladder having an inlet end and an outlet end for evacuating saidelastomeric bladder and for limiting force applied to the ceramicsuspension by the elastomeric bladder and being disposed within the moldcavity and distending during injection of the ceramic suspension, thedistention of the elastomeric bladder thereby applying a force to theceramic suspension which is sufficient to substantially prevent jettingof the ceramic suspension and formation of knit lines within the ceramicsuspension during injection of the ceramic suspension into theelastomeric bladder.
 21. An apparatus for injection molding a ceramicsuspension to form a molded ceramic greenware composite, comprising:a) amold defining a mold cavity; b) a water permeable elastomeric bladderwhich includes two sheets bonded together to form a peripheral seal, theelastomeric bladder being disposed within the mold cavity and having aninlet end for receiving the ceramic suspension and an outlet end forevacuating said elastomeric bladder and for limiting force applied tothe ceramic suspension by the elastomeric bladder; c) means forinjecting the ceramic suspension into said elastomeric bladder, wherebythe elastomeric bladder is distended, said distention of the elastomericbladder causing application of sufficient force to the ceramicsuspension to substantially prevent jetting of the ceramic suspensionand formation of knit lines within the ceramic suspension duringinjection of the ceramic suspension into the elastomeric bladder; and d)means for exposing the injected ceramic suspension to conditions whichare sufficient to form the molded ceramic greenware composite.
 22. Anapparatus for injection molding a ceramic suspension to form a moldedceramic greenware composite, comprising:a) a mold defining a moldcavity; b) an elastomeric bladder which includes two sheets bondedtogether to form a peripheral seal and having a permeability to watervapor of less than about one hundred forty grams per twenty-four hoursper one hundred square inch area at 50° C. per one mil thickness, theelastomeric bladder being disposed within the mold cavity and having aninlet end for receiving the ceramic suspension and an outlet end forevacuating said elastomeric bladder and for limiting the force appliedto the ceramic suspension by the elastomeric bladder; c) means forinjecting the ceramic suspension into said elastomeric bladder, wherebythe elastomeric bladder is distended, said distention of the elastomericbladder causing application of sufficient force to the ceramicsuspension to substantially prevent jetting of the ceramic suspensionand formation of knit lines within the ceramic suspension duringinjection of the ceramic suspension into the elastomeric bladder; and d)means for exposing the injected ceramic suspension to conditions whichare sufficient to form the molded ceramic greenware composite.